The present invention relates to branching equipment for CATV systems for distributing television signals from the main line of a CATV system to a number of branch lines.
In the CATV system, a television signal received by the community antenna is delivered to the main line from which the signal is distributed to a plurality of branch lines and then applied to the individual TV receivers. For this purpose, branching equipment is provided at various points of the main line and generally the branching equipment is of a simple type. It is known to use as a branching equipment, a distributing equipment of the type comprising a matching transformer consisting of a center-tapped winding whose one end serves as an input terminal and the other end is grounded and a distributing transformer consisting of a center-tapped winding whose ends are each adapted to serve as an output terminal and the center taps are interconnected whereby the signal applied to the input terminal is distributed to the output terminals at the same level. Since the ratio between the signal levels at the output terminals will be varied with a change in the turn ratio of the winding portions on both sides of the tap of the distributing transformer, this type of distributing equipment can be used as branching equipment by suitably selecting the turn ratio. If branching equipment comprising such distributing equipment is used for the purpose of distributing TV signals from the main line of a CATV system to the branch lines, there is the danger of a situation arising in which the leakage of the local oscillation signal from a TV receiver connected to one of the output terminals will result in interaction between the output terminals and this in turn will result in mutual interference between the leakage signal and the TV signal in the transmission line.
In the past, many different countermeasures have been proposed for the purpose of reducing such undesired signals and they have been unsatisfactory from the standpoint of both performance and construction due to the difficulty of ensuring the desired results in both the UHF and VHF bands, that is, the difficulty to ensure the desired reduction of undesired signals in a wide range of the bands, the necessity to use another tapped transformer as a balance transformer and so on.